Throughout this application various publications are referred to in parenthesis. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications are hereby incorporated by reference in their entireties into the subject application to more fully describe the art to which the subject application pertains.
There is a clinical need for new therapies for melanoma which is among the few cancers with a rising incidence (1). Malignant melanoma affects ˜40,000 new patients each year in the United States and an estimated 100,000 world-wide (2, 3). Melanoma is an important cause of cancer among young patients (30-50 years) which increases the economic importance of the disease. While primary tumors are successfully removed surgically, a satisfactory treatment for patients with metastatic melanoma has not been developed (4). The median survival time of patients with metastatic melanoma is 8.5 months, with an estimated 5-year survival of 6% (4). There has been little change in these results over the past 25 years.
Immune approaches to the therapy of metastatic melanoma have been evolving steadily and include treating patients with 1) non-specific immune stimulants with a focus on the use of tumor-associated antigens by passive immune therapy with antibodies targeted directly to tumor cells; and 2) active immune therapy via vaccination with tumor cells, tumor cell lysates, peptides, carbohydrates, gene constructs encoding proteins, or anti-idiotype antibodies that mimic tumor-associated antigens (5).
Monoclonal antibodies (mAbs) radiolabeled with diagnostic radioisotopes 99 m-Technetium (99mTc) and 111-Indium (111In) as well as with 131-Iodine (131I) have been used extensively for radioimmunoimaging (RII) of metastatic melanoma. A recent review by Kang and Yong (6) summarizes 58 patient trials (excluding case studies) involving a total of 3638 patients. The majority (>80%) of these studies used mAbs to high molecular weight melanoma associated antigen (HMW-MAA) proteoglycan. The sensitivity of RII using various anti-HMW-MAA mAbs or mAbs against other melanoma associated antigens such as P97 (7) is 65-88% (5, 6) which compares favorably with standard diagnostic methods (6). RII is also able to survey the entire body for metastases in a single study and can detect a substantial number of otherwise occult lesions.
Although RII has filled a niche in detection and disease assessment of metastatic melanoma, the ultimate goal is radioimmunotherapy (RIT). RIT takes advantage of the specificity of the antigen-antibody interaction to deliver lethal doses of radiation to target cells using radiolabeled antibodies (8). RIT is experiencing a renaissance, and so far has been most successful for the treatment of “liquid” and “semi-liquid” malignancies such as lymphoma and leukemia (9). The recent FDA approval of Zevalin® (IDEC Pharmaceuticals, San Diego, Calif.), which is 90-Yttrium (90Y) labeled monoclonal anti-CD20 antibody for treatment of relapsed or refractory B-cell non-Hodgkin's lymphoma is proof of the enormous potential of RIT in cancer treatment.
There have been relatively few attempts to use RIT for treatment of melanoma in either the pre-clinical or clinical settings. One possible explanation for this might be the perception of melanoma as a relatively radioresistant cancer (10, 11) resulting from the outcomes of radiation therapy of melanoma with external beam radiation. Radioresistance in melanoma has been associated with melanin contents which presumably provide a non-specific shield that absorbs photons. The perception that melanoma is radioresistant is changing now (11) and, more importantly, it has been shown that radioresistance of certain tumors towards external radiation beam is higher compared to treatment of the same type of tumors with radioimmunotherapy. The difference in efficacy is due to different mechanisms of interaction between tumor cells and gamma rays of external beam compared to the particulate radiation delivered by radiolabeled antibodies (12, 13). Significant killing of melanoma cells in monolayers was observed as a result of treatment with antibodies radiolabeled with 125-Iodine (14), 211-Astatine (15), and 111-Indium (16). 131-I-labeled mAb caused shrinkage of human malignant melanoma multicellular spheroids (17). In an animal model of human melanoma, intratumoral injection of mAb radiolabeled with alpha-emitter 213-Bismuth caused complete disappearance of xenografted tumors while systemic RIT was less efficient with some delay in tumor progression followed by eventual re-growth (18). In a pilot study in patients with metastatic melanoma (19), a patient who received total dose of 374 mCi 131-I-labeled Fab′ fragments of anti-HMW-MAA mAb showed a greater than 50% reduction in the size of pelvic and pericaval nodes, with stabilization of disease at the smaller nodal size for a period of several months.
The majority of human melanomas are pigmented with melanin. Although several antibodies have been tried for the therapy of melanomas (notably monoclonal antibodies against high molecular weight melanoma-associated antigen, against chondroitin sulfate proteoglycan, and against transferrin receptor), the approach of targeting melanin with an anti-melanin antibody has not been utilized. One factor which teaches away from the use of anti-melanin antibodies is that melanin is an intracellular pigment that is normally found in the melanosome. Hence, one might dismiss this pigment as a target as being inaccessible to a serum antibody. Another factor is that the amount of intracellular melanin is inversely related to the radiosensitivity of human melanoma cells (20-22). Melanin is thought to absorb radiation and thereby protect the cells.